Field
The invention relates to drug conjugates, compositions comprising the same, and methods of using such drug conjugates and compositions for the treatment of cancer and other diseases.
Description of the Related Art
VAR2CSA Protein
Proteoglycans are proteins conjugated to glycosaminoglycan (GAG) chains. These proteins are distributed inside cells, on the cell membrane and in the extracellular matrix serving a variety of functions: cartilage matrix formation; the structural organization of tissues; organizations of basement membranes; regulating the role of secretory vesicles; binding of cytokines, chemokines, growth factors, and morphogens; protease receptors and protease inhibitors; co-receptors, tyrosine-kinase-type growth factor receptors; as endocytic receptors; facilitate cell attachment, cell-cell interactions, and cell motility as well as cell migration.
The malaria parasite Plasmodium falciparum utilizes host cell proteoglycans in almost all stages of its complex life cycle. The sporozoite infects hepatocytes in the liver through surface-expressed circumsporozoite protein interacting with highly sulfated heparan sulfate proteoglycans (HSPG). Merozoite infection of the erythrocytes is mediated by EBA-175 binding to sialic acid on glycophorin A. In addition, a number of Plasmodium falciparum Erythrocyte Membrane Protein 1 (PfEMP1) proteins, mediating host endothelial adhesion, have been described as glycan-binding. One of these is VAR2CSA, which is a unique member of the PfEMP1 protein family. VAR2CSA binds with high affinity to a distinct form of chondroitin sulfate A (CSA), attached to proteoglycans, so called Chondroitin Sulfate Proteoglycan (CSPG), in the intervillous spaces of the placenta. This type of CSA is referred to as placental-like CSA (plCSA). VAR2CSA is a large multi-domain protein (350 kDa) expressed on the surface of P. falciparum-infected erythrocytes (IEs), and the VAR2CSA-plCSA interaction is responsible for placenta specific sequestration in placental malaria (PM). Importantly, recombinant full-length VAR2CSA ecto-domain from FCR3 and 3D7 type parasites has shown affinity for plCSA in the low nano-molar range.
CSA belongs to the family of glycosaminoglycans (GAGs), which are linear polymers of alternating amino sugars and hexuronic acid residues, attached to proteoglycans. There are several types of GAGs including; chondroitin sulfate (CS), dermatan sulfate (DS or CSB), heparan sulfate (HS) and heparin. While the polysaccharide backbone of these GAGs is simple, considerable diversity arises in modifications such as sulfation and uronate epimerization. This is the basis for the wide variety in domain structure and biological activities of different GAGs.
CS interacts with many important factors such as growth hormones, cytokines, chemokines, and adhesion molecules and is thought to be involved in structural stabilization, cytokinesis, cell proliferation, differentiation, cell migration, tissue morphogenesis, organogenesis, infection, and wound repair. CS chains are composed of alternating units of N-acetyl-D-galactosamine (GalNAc) and glucuronic acid residues. Glucuronic acid can be sulfated at its C2 position and GalNAc can be sulfated at C4 and/or C6, giving rise to various disaccharide units. Varying modifications of the sugar backbone allows structural and functional heterogeneity of the CS chains.
Chondroitin sulfate proteoglycan 4 (CSPG4), also known as High Molecular Weight-Melanoma Associated Antigen (HMW-MAA) or melanoma-associated chondroitin sulfate proteoglycan (MSCP), is a cell surface proteoglycan which has been shown to be expressed by melanoma cells. CSPG4/MSCP/HMW-MAA is a large proteoglycan characterized by having CS chains on the protein backbone.
VAR2CSA retains its ability to bind with high affinity and specificity to certain chondroitin sulfate proteoglycans with minimal structural elements of the polypeptide sequence. The core plCSA-binding site lies within the DBL2X domain including small parts of the flanking interdomain regions. The binding does not depend on the ID2b region, or on the DBL1X or DBL3X flanking domains, as previously suggested. The minimal binding region is ID1-DBL2Xb, which binds CSPG with characteristics comparable to that of full-length VAR2CSA. The ID1-DBL2Xb minimal binding region is much smaller than full-length VAR2CSA, having a molecular weight of only 62 kDa. This VAR2CSA fragment and other VAR2CSA polypeptides bind with high and specific affinity to cancer cells and tissues, which binding is suggested to be through a specific interaction with chondroitin sulfate proteoglycans expressed on the surface of the cancer cells or in the surrounding extracellular matrix (Salanti et al., WO2013/117705). Accordingly, this specific and high affinity binding may be used for the targeting of cancer cells or other tissues or cells with high or otherwise expression, such as inappropriate expression, of this particular type of chondroitin sulfate proteoglycan.
In the medical field, there is a need for stable protein-drug conjugates that can release biologically active compounds selectively at desired target locations having high, or otherwise inappropriate, expression of chondroitin sulfate proteoglycans. The present disclosure fulfills these needs and provides further related advantages.